Prevention of hydrogen embrittlement

ABSTRACT

A METHOD OF PREVENTING HYDROGEN EMBRITTLEMENT OF PARTS WHICH ARE NORMALLY PROTECTED FROM CORROSION BY SACRIFICAL COATINGS WHOSE CATHODIC CORROSION PROTECTION REACTION RESULTS IN FREE HYDROGEN, BY INCLUDING A RARE EARTH METAL IN THE COATING PROCESS WHICH ACTS AS A HYDROGEN GETTER TO PROVENT THE HYDROGEN GENERATED FROM PENETRATING AND EMBRITTLING THE CORROSION PROTECTED PART.

United States Patent Oflice 3,823,075 Patented July 9, 1974 3,823,075 PREVENTION OF HYDROGEN EMBRI'I'ILEMENT Austin Phillips, Santa Monica, Calif., assignor to McDonnell Douglas Corporation No Drawing. Filed Dec. 28, 1971, Ser. No. 213,157 Int. Cl. C2315 17/00; B01k 3/00 US. Cl. 20438 B 15 Claims ABSTRACT OF THE DISCLOSURE A method of preventing hydrogen embrittlement of parts which are normally protected from corrosion by sacrificial coatings whose cathodic corrosion protection reaction results in free hydrogen, by including a rare earth metal in the coating process which acts as a hydrogen getter to prevent the hydrogen generated from penetrating and embrittling the corrosion protected part.

CROSS-REFERENCE TO RELATED APPLICATION This application relates to the subject matter of US. Pat. Application entitled Rare Earth Hydrogen Detector, by Stephen M. Toy and Austin Phillips, Ser. No. 155,019, now US. Pat. No. 3,732,076, which was filed June 21, 1971 and assigned to Applicants assignee and reference is made to the information therein as though fully set forth hereinbelow.

BACKGROUND OF THE INVENTION When hydrogen enters steel and certain other metals and alloys, it may cause severe embrittlement of these materials. If large quantities of hydrogen are introduced the hydrogen causes a severe loss in ductility and degradation of mechanical properties. It has been recognized that conventional cadmium plating or other types of plating, wherein the plating material sacrifices itself in a cathodic reaction to protect the plated part from corrosion, can cause severe embrittlement since free hydrogen is a product of the protection reaction. Since the reaction continues after the part has been placed in service, the embrittlement caused by the hydrogen cannot always be eliminated by baking which heretofore has been the usual method to prevent hydrogen embrittlement of a part. Therefore, a method has been required which can prevent embrittlement of a part even after it is in service.

BRIEF DESCRIPTION OF THE INVENTION The present invention permits prevention of hydrogen embrittlement even when the part sensitive to hydrogen embrittlement is plated by a material which generates free hydrogen. The invention comprises including rare earth metal adjacent the surface of the part. The rare earth metal acts as a getter of hydrogen and thereby prevents the hydrogen generated in the cathodic corrosion protection reaction from entering the crystal structure of the protected part to thereby prevent hydrogen embrittlement.

It is therefore an object of the present invention to prevent the hydrogen embrittlement of plated parts.

Another object of the present invention is to eliminate the need for baking hydrogen out of fabricated parts which are sensitive to hydrogen embrittlement.

Another object is to provide a method of preventing hydrogen embrittlement which is adaptable to many types of materials and environments in which they operate.

These and other objects and advantages of the present invention will become apparent after considering the following detailed specification which covers preferred embodiments thereof.

DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTS The present method for preventing hydrogen embrittlement is primarily for use in preventing embrittlement of plated high strength materials. The method prevents the injection of hydrogen into the hydrogen sensitive part whether the hydrogen is generated during the plating process or later in its corrosion protection reaction.

The invention utilizes the fact that rare earth metals readily form hydrides near room temperature and therefore can be utilized as hydrogen getters. Since neodymium forms a hydride in the region of 29 C. and cesium forms a hydride from 20 to C., they, along with praseodymium and yttrium, provide the better rare earth metals for the present invention when the part protected is going to be exposed to hydrogen near ambient temperatures.

The rare earth metal may be applied asa layer to the part to be plated in a two step coating process as in Example 1.

Example 1 Two specimens of high strength steel (4340, 260/280 k.s.i.) with abraded surfaces were prepared; one with an approximately 300 A. thick film of neodymium plus a film of copper on the outside thereof to prevent oxidation of neodymium and one with the copper film only. Both the neodymium and copper films were vacuum deposited. Then both specimens were electrochemically plated with cadmium by the normal aqueous process. As shown in Table l, the specimen with the neodymium plus copper film showed remarkably high ductility without any baking to drive off hydrogen although baking for 24 hours at 375 F. is the normal procedure. The specimen without neodymium showed virtually no ductility. The fracture appearance of the specimen with the neodymium plus copper film showed a 45 ductile break While the specimen without neodymium showed a flat brittle break.

A light sand blast produced the following mechanical properties:

Fty (k.s.i.) Percent Spec. .2% ofiset Fm (k.s.l.) E., 2 IN.

Nd+Cu+Cd 217. 6 255. 1 6 Cu-l-Cd 215. 1 254. 6 4

The testing rate in all cases was 5,000 lb./min.

The above example demonstrated that neodymium and any similar rare earth metal can act as a barrier to hydrogen entering metals or other alloys and can prevent hydrogen embrittlement. Processes according to the above example can eliminate the costly baking procedure now required after the plating process but due to the vacuum deposition step, the process is not particularly adaptable to large parts and therefore the cost saving is considerably reduced.

Other possibilities of applying the method have been developed such as adding the rare earth metal as a salt to a nonaqueous plating bath solution, coplating the rare earth metal cadmium, introducing the rare earth metal in the form of a plasma jet, difiusing the rare earth metal into the surface of the base material before plating, and adding the rare earth metal as an alloy element in the plating vacuum deposition. of these the most promising processes from economy standpoints seem to be alloy vacuum deposition and nonaqueous plating.

Example 2 x 20 4340 notched steel studs, 2 inches long were placed as cathodes in an electrolyte consisting of:

34 gms. (.lM) of Nd and 180 gms. (3.0M) of OO(NH urea at a temperature of 245 F. Carbon anodes were used and the plating proceeded as follows:

Current density, Nd deposit Time, amps/ Voltage, thickness, minutes sq. it. v. inch 90 5 Flash 190 8 5X10' Other studs were placed as cathodes in an electrolyte consisting of:

gms. (.1M) of NdF and 180 gms. (3.0M) of CO(NH urea at a temperature of 255 F. Carbon anodes were again used and the plating proceeded as follows:

Time, min. 5 Voltage 4 Nd Deposit Thickness flash Still other studs were placed as the cathodes in an electrolyte consisting of:

24.6 gms. (.lM) of CeCl and 220 gms. (3.5M) of CO(NH urea at a temperature of 250 F. Carbon anodes were used and the plating proceeded as follows:

Time 5 min Current Density 180 Amps/sq.ft. Voltage 17 Ce Deposit Thickness 1X10" inch After rare earth plating, the studs were cadmium plated by placing them as cathodes in an electrolyte made from:

17 gms. (.lM) of CdSO -8H O, and 180 gms. (3.0M) of CO(NH urea at a temperature of 250 F. Carbon anodes were used and the plating proceeded as follows:

Current density, I Cd deposlt Time, amps/ Voltage, thieknesss minutes sq. ft. v. inch In all cases, there was no discernible difierence in appearance between the rare earth-cadmium plated studs and control studs cadmium plated in a conventional aqueous cadmium plating process.

Two studs having a 5 10- inch Nd plate and a 1.5 x 10- Cd plate and two studs having a 1.5 10- inch Cd plate conventionally applied were placed in a sustained load test with the load at 90% of ultimate. None of the studs were baked. The conventionally plated Cd specimens broke at 12 and 16 hours showing diffusion of hydrogen to high stress areas therein to cause the failures. The Nd-Cd plated specimens withstood the sustained load 4 without any measurable harm for 266 hours at which time the test was arbitrarily stopped. The above testing proved that nonaqueous rare earth-Cd plating processes are as effective as the vapor deposition in the reduction of hydrogen embrittlement.

Although urea was used as the solvent in the nonaqueous plating process, many other nonaqueous polar solvents can be used including formamide; N,N-dimethylformamide; acetamide; N,N dimethylacetamide; acetonitrile; dimethylsulfoxide; and dimethylsulfone.

Thus there has been shown and described a novel method for preventing hydrogen embrittlement which fulfills all of the objects and advantages sought therefor. Many changes, alterations, modifications and other uses and applications of the present invention will become apparent to those skilled in the art after considering this specification. All such changes, modifications, variations, and other uses and applications which do not depart from the spirit and scope of the present invention are deemed to be covered by the invention which is limited only by the claims which follow.

What is claimed is:

1. A method of reducing hydrogen embrittlement of items to be protected from corrosion by sacrificial coatings whose cathodic corrosion protection reaction produces free hydrogen, said method comprises applying at least one rare earth metal on the surface of the item either before or during application of said sacrificial coating, said rare earth metal acting as a hydrogen getter to reduce the free hydrogen available to embrittle the corrosion protected item.

2. The method described in Claim 1 wherein a layer of rare earth metal is applied to the surface of the item in an electrochemical plating process using a nonaqueous solvent and at least one rare earth salt as electrolyte.

3. The method defined in Claim 2 wherein said item is thereafter coated with said sacrificial coating in an electrochemical plating process using a nonaqueous solvent as the major constituent of the electrolyte.

4. The method defined in Claim 2 wherein said nonaqueous solvent is chosen from a group consisting of urea, formamide, N,N-dimethylformamide, acetamide, N,N-dimethylacelamide, acetonitrile, dimethylsulfoxide, and dimethylsulfone.

5. The method described in Claim 1 wherein said rare earth metal is vacuum deposited on the surface of the item.

6. The method described in claim 5 wherein a protective layer of metal is deposited over said rare earth metal after which said item is coated with said sacrificial coating.

7. The method described in Claim 1 wherein said rare earth metal is chosen from the group consisting of cerium, neodymium, praseodymium and yttrium.

8. The method defined in Claim 1 wherein said sacrificial coating is a cadmium plate.

9. The method defined in Claim 1 wherein a rare earth metalsacrificial coating alloy is vacuum deposited on said items surface.

'10. The method of reducing hydrogen embrittlement of a hydrogen sensitive item, said method comprising coating at least one rare earth metal chosen from the group consisting of cerium and neodymium on the surface of the item and applying a protective coating thereover, said rare earth metal acting as a hydrogen getter by forming rare earth hydrides thereby reducing the amount of free hydrogen available to embrittle the hydrogen sensitive item.

11. The method described in Claim 10 wherein said rare earth metal is 'vacuum deposited on the surface of the item.

12. The method described in Claim 10 wherein a layer of rare earth metal is applied to the surface of the item in an electrochemical plating process using a nonaqueous solvent and at least one rare earth salt as electrolyte.

13. The method defined in Claim 12 wherein said item is thereafter coated with a layer of metal in an electrochemical plating process using an nonaqueous solvent as the major constituent of the electrolyte.

'14. The method defined in Claim 12 wherein said nonaqueous solvent is chosen from a group consisting of urea, formamide, N,N-dimethylformamide, acetamide, N,N-dimethylacelamide, acetonitrile, dimethylsulfoxide, and dimethylsulfone.

15. A method of reducing hydrogen embrittlement of items protected from corrosion by sacrificial coatings whose cathodic corrosion protection reaction produces free hydrogen, said method comprises diflfusing at least one rare earth metal into the surface of the item and coating said item with said sacrificial coating.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner US. Cl. X.R. 

